gh-142349: Implement PEP 810 #142351

pablogsal · 2025-12-06T15:45:47Z

Issue: Implement PEP 810 #142349

⚠️ Dear reviewers, to avoid collapsing the GitHub API with a lot of comments, please open PRs against the base branch with any suggestions or fixes if you are sure are not controversial ⚠️

📚 Documentation preview 📚: https://cpython-previews--142351.org.readthedocs.build/

…s on bad usage of lazy

Highlight lazy imports in the new REPL

picnixz · 2025-12-06T18:33:10Z

I'll be doing small reviews because I'm not on my dev session and it takes too long for creating a PR :') I promise I won't be too nitpicky!

StanFromIreland · 2025-12-06T18:53:06Z

Doc/reference/simple_stmts.rst

   pair: name; binding
   pair: keyword; from
   pair: keyword; as
+   pair: keyword; lazy


I suggest you move this to the below section on lazy specifically.

picnixz

I'll review more tomorrow when I'm on my dev session, it'll be easier. But here are a few comments and questions about import.c

Python/import.c

picnixz · 2025-12-06T18:40:41Z

Python/import.c

+    PyObject *old = _Py_atomic_exchange_ptr(&LAZY_IMPORTS_FILTER(interp), Py_XNewRef(filter));
+    Py_XDECREF(old);
+#else
+    Py_XSETREF(LAZY_IMPORTS_FILTER(interp), Py_XNewRef(filter));


This makes me wondeer whether we couldn't have a FT helper for this. It's probably not the only place that will need this in the future.

Python/import.c

picnixz · 2025-12-06T18:45:24Z

Python/import.c

+
+    // Add the module name to sys.lazy_modules set (PEP 810)
+    PyObject *lazy_modules_set = interp->imports.lazy_modules_set;
+    if (lazy_modules_set != NULL) {


When is it possible to have lazy_modules_set NULL?

Python/import.c

Parser/action_helpers.c

StanFromIreland · 2025-12-06T19:00:18Z

Doc/reference/simple_stmts.rst

+
+   lazy import json


Suggested change

lazy import json

lazy import json

lazy import sys

For 'json' in sys.modules to run.

pablogsal · 2025-12-06T19:02:36Z

@DinoV @colesbury I haven't paid attention to FT when I updated the draft implementation so please take a special look at that

pablogsal · 2025-12-06T19:07:44Z

@DinoV @colesbury I haven't paid attention to FT when I updated the draft implementation so please take a special look at that

In particular ./python -m test test_import.test_lazy_imports -v shows some tsan problems.

I think I got them in 470b9e4 but not sure if that's the best way to fix this.

Include/internal/pycore_magic_number.h

StanFromIreland · 2025-12-07T09:48:38Z

Lib/test/test_import/test_lazy_imports.py

+    def test_global_off(self):
+        """Mode 'none' should disable lazy imports entirely."""
+        import test.test_import.data.lazy_imports.global_off
+        self.assertTrue("test.test_import.data.lazy_imports.basic2" in sys.modules)


We can use assertIn instead, a suggestion that applies for all cases: LazyImportsCabal#27

StanFromIreland · 2025-12-07T09:49:35Z

Lib/test/.ruff.toml

    # New grammar constructions may not yet be recognized by Ruff,
    # and tests re-use the same names as only the grammar is being checked.
    "test_grammar.py",
+    # Lazy import syntax (PEP 810) not yet supported by Ruff


Suggested change

# Lazy import syntax (PEP 810) not yet supported by Ruff

# Lazy import syntax (PEP 810) is not yet supported by Ruff

picnixz · 2025-12-07T09:59:00Z

@StanFromIreland assertIn/assertNotIn is addressed in LazyImportsCabal#28

StanFromIreland · 2025-12-07T10:13:11Z

Great minds think alike;-) I had opened LazyImportsCabal#27 for it.

picnixz · 2025-12-07T10:17:05Z

There was also an hasattr check thatq we could change and I also changed import order to make them alphabetically sorted. Do you mind merging my PR in yours?

StanFromIreland · 2025-12-07T10:27:11Z

Do you mind merging my PR in yours?

Done :-)

picnixz · 2025-12-07T11:00:14Z

@pablogsal

PEP-7 nits in import.c: Apply PEP-7 to Python/import.c LazyImportsCabal/cpython#29
Docs fixes: Document return value for PyImport_GetLazyImportsFilter LazyImportsCabal/cpython#32
PR fixing UAFs/error paths in import.c: Fix UAFs and error paths in import.c LazyImportsCabal/cpython#30
PR for fixing lazy_import.__new__ and UBs: Fix and improve Objects/lazyimportobject.c LazyImportsCabal/cpython#31
PR fox fixing UAFs/error paths in Python/*.c: Various UAFs & cosmetic fixes in Python/{bltinmodule,bytecode,ceval}.c LazyImportsCabal/cpython#33
PR for fixing the compilation issues in the CI: Fix missing lazy-related symbols for the JIT LazyImportsCabal/cpython#34

There are other places where PEP-7 is not applied but I won't bother changing those places if I'm not changing the effective code as well. Ideally, I should add tests for checking that my UAFs fixes are correct but we can do it once they're reviewed and merged.

DinoV and others added 30 commits October 2, 2025 13:22

Lazy imports grammar / AST changes

1c691ea

Add __lazy_import__, check sys.modules before import

3b0d745

Export lazy_import in imp module

9eef03c

Add lazy import filter

de281fd

Add compatiblity mode

41ab092

Flow import func through to lazy imports object and __lazy_import__

058bc6e

Reify lazy objects when accessed via the module object

6d7c87a

Import lazy.get

f992ee7

Implement better error

6a91132

Fix reference and global dict in spezializing LOAD_GLOBAL

03a419a

Remove copyright

e0878be

More fixes

f9880bf

Fix recursive lazy imports and error path in bytecodes.c

f3f5795

fix offset in addr2line

44a3e46

Add global flag

73de8d0

Draft: force * imports to be eager

07a633f

Syntax restrictions for lazy imports

20b14d9

Fix submodules crash

164423b

Implement disabling imports in try/except and * imports, report error…

00e7800

…s on bad usage of lazy

Add PyExc_ImportCycleError and raise it when a cycle is detected

781eedb

Publish lazy imported packages on parent

9be59ec

Re-enable eagerly returning imported module

b179da2

Fix __lazy_modules__

9078f57

Add sys.set_lazy_imports_filter

f67310c

Simplify grammar

39c33df

Move __lazy_imports__ check into the interpreter

c8c8838

Don't allow __lazy_imports__ to work in try/except

7c49405

Make imports in with blocks syntax errors

5d6026a

Highlight lazy imports in the new REPL

c0c0d80

Merge pull request #2 from bswck/lazy-import-pyrepl-highlight

5ff0dd2

Highlight lazy imports in the new REPL

Doc updates

0985e2a

pablogsal requested a review from willingc as a code owner December 6, 2025 18:34

pablogsal and others added 5 commits December 6, 2025 18:37

Address feedback

610af78

More doc fixes

917b92e

Make error for invalid lazy from __future__ ... import prettier

e777866

Regen limited ABI

952ac21

Merge branch 'lazy' into lazy-future-error

33dc19e

StanFromIreland reviewed Dec 6, 2025

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picnixz reviewed Dec 6, 2025

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StanFromIreland reviewed Dec 6, 2025

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Parser/action_helpers.c Outdated Show resolved Hide resolved

Fix error paths and edge cases

80133a5

StanFromIreland reviewed Dec 6, 2025

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Free threading fixes

b0adc30

picnixz reviewed Dec 6, 2025

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Include/internal/pycore_magic_number.h Outdated Show resolved Hide resolved

pablogsal and others added 5 commits December 6, 2025 19:16

TSAN fixes

470b9e4

Update magic number

41761e5

Merge pull request #26 from StanFromIreland/lazy-future-error

74b3efe

Regen frozenmain

006ca9c

Fix WASI failure

b5121b0

StanFromIreland reviewed Dec 7, 2025

View reviewed changes

AlexWaygood removed their request for review December 7, 2025 10:47

	# Lazy import syntax (PEP 810) not yet supported by Ruff
	# Lazy import syntax (PEP 810) is not yet supported by Ruff

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gh-142349: Implement PEP 810 #142351

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gh-142349: Implement PEP 810 #142351

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